1. Field of the Invention
The invention relates to a process for preparing 2-oxo-dihydrobenzo[d][1,3]-oxazines (also named 1,4-dihydro-2H-3,1-benzoxazin-2-ones) and to the conversion of those products to the corresponding 2-amino-benzyl alcohols which are useful as intermediates in the production of pharmaceuticals, herbicides and dyestuffs.
2. Description of the Prior Art
In chemical synthesis, when it is desired to prepare an aniline, it is usual to employ one of two general approaches, one being the Hofmann rearrangement of benzamides, and the other being the hydrogenation of nitrobenzenes. However both of these approaches run into great difficulties when applied to the preparation of 2-amino-benzyl alcohols, either the unsubstituted compound or a substituted derivative thereof, due to side reactions involving the reactive --CH.sub.2 OH group. In the case of a Hofmann rearrangement, internal nucleophilic attack by the --CH.sub.2 OH group may result in the formation of a phthalide, or oxidation of the --CH.sub.2 OH group may result in benzaldehydes and benzoic acids. In a hydrogenation reaction the --CH.sub.2 OH group may be hydrogenated to a methyl group.
As far as is known, the only 2-amino-benzyl alcohol in commercial production is 2-amino-benzyl alcohol itself, and neither of the above approaches has been used in its preparation. It has previously been found necessary to resort to the reduction of anthranilic acid using lithium aluminum hydride, but lithium aluminum hydride is an expensive reagent and is notoriously difficult to handle on any scale, particularly because of its tendency to cause fires.
Graebe et al. Chem. Ber. 35, 2751-52 (1902) describes the conversion of salicylamide by alkaline hypochlorite to 4,5-benzoxazolone.
Lindemann et al. Ann. Chem. 464, 245-7 (1928) describes the conversion of 2-hydroxymethyl-2-benzoylazide in refluxing benzene to 2-oxo-dihydrobenzo[d][1,3]oxazine and hydrolysis of the latter with sodium hydroxide to 2-aminobenzyl alcohol.
Aelony et al. U.S. Pat. No. 3,705,154 describes the thermolytic conversion of trimethylammonium-N-(2-hydroxymethylbenzoyl)-imine to 2-oxo-dihydrobenzo[d][1,3]oxazine.
Starks J. Amer. Chem. Soc. 93, 195 (1971) and Dehmlow Angew. Chem., Int. Ed. English 13, 170 (1974) describe the use of quaternary ammonium and phosphonium salts as phase transfer catalysts in two-phase reactions.
Lee et al. Tetrahedron Lett. 1976, 1641-44 describes the phase transfer catalyzed oxidations of alcohols and amines by aqueous hypochlorite.